> The internal diodes cannot protect from these spikes.
> ......
> That application note has always amased me because it is just pure bad
> enginnering.

Let's see, the PIC input diodes can take about 20mA (I'm guessing).

With a 100K resistor, that's 2KV input
With 1Meg  that's 20 KV .

And BTW, that's continuous current.
For narrow pulses, the PIC could handle proportionally more current.

My point is that the resistor will die long before the PIC !
(a 1 Meg resistor with 20 KV across it is dissipating 400 Watts !!)

And of course you would have a small cap at the PIC to filter out the HF
junk.
This cap would  also greatly limit any spikes.

The weakest link would be the voltage rating of the resistor, you would need
a couple in series at least.
And yes, I personally would put a MOV or something at the junction of the
resistors.

Just pointing out that the App note isn't crazy when you actually do the
sums...

..................... Zim

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